1. Field of the Invention
The invention relates to a double walled riser containment sump and reservoir suitable for use with underground storage tanks.
2. Discussion of the Background
Underground storage tanks are used in a wide variety of locations to store materials underground. The stored materials are often harmful to the environment. Examples of such materials include gasoline and other petroleum products, e.g., oil and waste oil, as well as toxic raw materials and waste from manufacturing processes. Because of the harmful nature of these materials, it is especially important to ensure that underground storage tanks containing such materials do not leak or release these materials into the environment.
Concern over this possibility has lead many governmental authorities to require secondary containment for tanks that store such materials. One of the most common methods for providing secondary containment is through the use of double walled underground storage tanks. The assignee of the present application, Xerxes Corporation, has manufactured and sold double walled underground storage tanks prepared from corrosion resistant materials such as fiber reinforced plastic (FRP) since 1984. These tanks have proven very reliable.
However, no matter how reliable the underground storage tank itself is, there is always the possibility that the pipes connected to the tank may fail. In recognition of this possibility, the use of double-walled piping has come into practice. Double walled piping includes an inner wall separated from an outer, or second, wall. The inner wall provides a passage for fluid between the inside of the underground storage tank and a desired destination. The outer wall of the double walled piping prevents any fluid escaping from a breach in the inner wall from leaking into the ground, thereby providing the secondary containment function.
Double walled piping installations typically include a riser containment sump in fluid communication with the annulus formed by the two walls of the piping so fluid leaking from the inner wall of the pipe will be carried by the outer wall to and contained by the riser sump. The most common type of this containment sump is formed by a riser extending from the storage tank. An example of a double-walled piping/underground storage tank installation with such a single wall sump is illustrated in U.S. Pat. No. 4,639,164 to Pugnale et al. A sensor is typically placed at the bottom of the sump so that any leaks are detected. In order for the sump to function properly, the sump must be watertight. An exemplary water-tight riser is described in U.S. Pat. No. 5,595,456, also assigned to Xerxes Corp.
It has been recognized that the ability of the system to contain leaks will be compromised if the sump leaks. To rectify this problem, the California legislature has required that sumps be either tested periodically or continuously monitored.